One of the important key performance indicators of new radio (NR) technology is control plane latency from a power efficient state to a data transmission state. Preferably, the latency would be less than 10 milliseconds. For NR, a new radio resource control (RRC) state has been introduced to satisfy the above described purpose. Conventionally, RRC states include a RRC connected state during which an electronic device is connected to the network and a RRC idle state during which the electronic device is not connected to the network and could be in a power off state or a sleep state. Recently, a new RRC state in addition to the above described RRC states has been proposed, and the new state is referred to as the “RRC inactive state” (RRC_INACTIVE). The RRC inactive state could be implemented within a network which utilizes the NR technology, and such network would be introduced as follows.
FIG. 1 illustrates a hypothetical next generation (NG) radio access network (RAN), or NG-RAN for implementing RAN-based notification area (RNA). The network may include a Core Network (CN) 101 communicating with a NG-RAN. The CN 101 is assumed to include a control plane (CP) controller (or anchor) 102 and a user plane (UP) controller (or anchor) 103. Although the NG-RAN has not adopted the concept of Anchor nodes and Candidate nodes, for illustration purposes, the NG-RAN of FIG. 1 is assumed to include an Anchor Node 111 and at least one Candidate Node 112 113. The Anchor Node is a node that maintains a CP connection 104 and a UP connection 105 to the CN 101 while a UE 121 connects to a cell belonging to it in the active state. The RAN-based Notification Area (RNA) is the area that the UE 121 is configured to perform the mobility without notifying the network. For instance, the RNA may include not limited to the coverage range of the Anchor node 111 and the Candidate Nodes 112 113. The UE 121 may select a cell within the RNA to connect to the NG-RAN while the UE 121 has UL data to be transmitted. A Candidate Node 111 is a node that corresponds to a cell including in the RAN-based notification area. At least a cell including in the RAN-based notification belongs to the Anchor Node. The CP anchor 102 is an entity within the CN 101 to interact with the CP such as a mobility management entity (MME) in the Evolved Packet Core (EPC). The UP anchor 103 is an entity of the CN 101 to interact with the data plane such as a serving gateway (S-GW) in the EPC. A connecting node (e.g. 111, 112 113) could be any node which the UE connects to within the RNA by performing a random access (RA) procedure.
The RRC inactivate state is a state where a mobile electronic device or user equipment (UE) may move within an area configured by a NG-RAN without notifying the NG-RAN. Also under such state, the anchor node may keep the UE context and the UE-associated NG connection with the serving AMF (Access and Mobility Management Function) and UPF (User Plane Function). The UE 121 would notify the network if the UE 121 moves out of the configured RNA. Thus, the characteristics of the RRC inactive state would include maintaining connections of both CP 104 and UP 105 between the NG-RAN and the CN 101 for associated the UE in the RRC inactivate state. Also under such state, a NG-RAN initiated notification procedure would be used to reach UE 121. Further, notification related parameters would be configured by the NG-RAN itself. When the UE 121 is in the RRC inactive state, the NG-RAN would be aware of the UE 121 moving from one RNA to another.
To order to implement the RRC inactive state, there are currently unresolved issues. For instance, it is uncertain under which circumstance a UE in general would be configured to enter the RRC inactive state from a network's point of view. How RNAs could be arranged have not been specified. Moreover, it is unclear how to process the tradeoff between network burdens and UE power consumptions. Considering the uncertainties, a mechanism for a UE to switch between a RRC connection state and a RRC inactive state to address the above described issues would still need to be proposed.